diff --git a/targets/TARGET_NUVOTON/TARGET_M251/mbed_overrides.c b/targets/TARGET_NUVOTON/TARGET_M251/mbed_overrides.c
index 85fddf7ffb..db926f3436 100644
--- a/targets/TARGET_NUVOTON/TARGET_M251/mbed_overrides.c
+++ b/targets/TARGET_NUVOTON/TARGET_M251/mbed_overrides.c
@@ -48,12 +48,18 @@ void mbed_sdk_init(void)
 #if MBED_CONF_TARGET_HXT_PRESENT
     /* Enable HXT clock (external XTAL 12MHz) */
     CLK_EnableXtalRC(CLK_PWRCTL_HXTEN_Msk);
+#else
+    /* Disable HXT clock (external XTAL 12MHz) */
+    CLK_DisableXtalRC(CLK_PWRCTL_HXTEN_Msk);
 #endif
     /* Enable LIRC */
     CLK_EnableXtalRC(CLK_PWRCTL_LIRCEN_Msk);
 #if MBED_CONF_TARGET_LXT_PRESENT
     /* Enable LXT */
     CLK_EnableXtalRC(CLK_PWRCTL_LXTEN_Msk);
+#else
+    /* Disable LXT */
+    CLK_DisableXtalRC(CLK_PWRCTL_LXTEN_Msk);
 #endif
 
     /* Wait for HIRC clock ready */
diff --git a/targets/TARGET_NUVOTON/TARGET_M261/mbed_overrides.c b/targets/TARGET_NUVOTON/TARGET_M261/mbed_overrides.c
index 3d988ce8bb..fb53f6c15c 100644
--- a/targets/TARGET_NUVOTON/TARGET_M261/mbed_overrides.c
+++ b/targets/TARGET_NUVOTON/TARGET_M261/mbed_overrides.c
@@ -39,12 +39,18 @@ void mbed_sdk_init(void)
 #if MBED_CONF_TARGET_HXT_PRESENT
     /* Enable HXT clock (external XTAL 12MHz) */
     CLK_EnableXtalRC(CLK_PWRCTL_HXTEN_Msk);
+#else
+    /* Disable HXT clock (external XTAL 12MHz) */
+    CLK_DisableXtalRC(CLK_PWRCTL_HXTEN_Msk);
 #endif
     /* Enable LIRC */
     CLK_EnableXtalRC(CLK_PWRCTL_LIRCEN_Msk);
 #if MBED_CONF_TARGET_LXT_PRESENT
     /* Enable LXT */
     CLK_EnableXtalRC(CLK_PWRCTL_LXTEN_Msk);
+#else
+    /* Disable LXT */
+    CLK_DisableXtalRC(CLK_PWRCTL_LXTEN_Msk);
 #endif
     /* Enable HIRC48 clock (Internal RC 48MHz) */
     CLK_EnableXtalRC(CLK_PWRCTL_HIRC48EN_Msk);
diff --git a/targets/TARGET_NUVOTON/TARGET_M451/mbed_overrides.c b/targets/TARGET_NUVOTON/TARGET_M451/mbed_overrides.c
index 7e9a231eb5..5571cd2998 100644
--- a/targets/TARGET_NUVOTON/TARGET_M451/mbed_overrides.c
+++ b/targets/TARGET_NUVOTON/TARGET_M451/mbed_overrides.c
@@ -36,12 +36,18 @@ void mbed_sdk_init(void)
 #if MBED_CONF_TARGET_HXT_PRESENT
     /* Enable HXT clock (external XTAL 12MHz) */
     CLK_EnableXtalRC(CLK_PWRCTL_HXTEN_Msk);
+#else
+    /* Disable HXT clock (external XTAL 12MHz) */
+    CLK_DisableXtalRC(CLK_PWRCTL_HXTEN_Msk);
 #endif
     /* Enable LIRC */
     CLK_EnableXtalRC(CLK_PWRCTL_LIRCEN_Msk);
 #if MBED_CONF_TARGET_LXT_PRESENT
     /* Enable LXT */
     CLK_EnableXtalRC(CLK_PWRCTL_LXTEN_Msk);
+#else
+    /* Disable LXT */
+    CLK_DisableXtalRC(CLK_PWRCTL_LXTEN_Msk);
 #endif
 
     /* Wait for HIRC clock ready */
diff --git a/targets/TARGET_NUVOTON/TARGET_M480/mbed_overrides.c b/targets/TARGET_NUVOTON/TARGET_M480/mbed_overrides.c
index ca21d76fb6..986a3f8d05 100644
--- a/targets/TARGET_NUVOTON/TARGET_M480/mbed_overrides.c
+++ b/targets/TARGET_NUVOTON/TARGET_M480/mbed_overrides.c
@@ -38,12 +38,18 @@ void mbed_sdk_init(void)
 #if MBED_CONF_TARGET_HXT_PRESENT
     /* Enable HXT clock (external XTAL 12MHz) */
     CLK_EnableXtalRC(CLK_PWRCTL_HXTEN_Msk);
+#else
+    /* Disable HXT clock (external XTAL 12MHz) */
+    CLK_DisableXtalRC(CLK_PWRCTL_HXTEN_Msk);
 #endif
     /* Enable LIRC */
     CLK_EnableXtalRC(CLK_PWRCTL_LIRCEN_Msk);
 #if MBED_CONF_TARGET_LXT_PRESENT
     /* Enable LXT */
     CLK_EnableXtalRC(CLK_PWRCTL_LXTEN_Msk);
+#else
+    /* Disable LXT */
+    CLK_DisableXtalRC(CLK_PWRCTL_LXTEN_Msk);
 #endif
 
     /* Wait for HIRC clock ready */
diff --git a/targets/TARGET_NUVOTON/TARGET_NANO100/mbed_overrides.c b/targets/TARGET_NUVOTON/TARGET_NANO100/mbed_overrides.c
index 8a6c946e0b..a88d2b52e8 100644
--- a/targets/TARGET_NUVOTON/TARGET_NANO100/mbed_overrides.c
+++ b/targets/TARGET_NUVOTON/TARGET_NANO100/mbed_overrides.c
@@ -36,12 +36,18 @@ void mbed_sdk_init(void)
 #if MBED_CONF_TARGET_HXT_PRESENT
     /* Enable HXT clock (external XTAL 12MHz) */
     CLK_EnableXtalRC(CLK_PWRCTL_HXT_EN_Msk);
+#else
+    /* Disable HXT clock (external XTAL 12MHz) */
+    CLK_DisableXtalRC(CLK_PWRCTL_HXT_EN_Msk);
 #endif
     /* Enable LIRC clock (OSC 10KHz) */
     CLK_EnableXtalRC(CLK_PWRCTL_LIRC_EN_Msk);
 #if MBED_CONF_TARGET_LXT_PRESENT
     /* Enable LXT clock (XTAL 32KHz) */
     CLK_EnableXtalRC(CLK_PWRCTL_LXT_EN_Msk);
+#else
+    /* Disable LXT clock (XTAL 32KHz) */
+    CLK_DisableXtalRC(CLK_PWRCTL_LXT_EN_Msk);
 #endif
 
     /* Wait for HIRC clock ready */
diff --git a/targets/TARGET_NUVOTON/TARGET_NUC472/mbed_overrides.c b/targets/TARGET_NUVOTON/TARGET_NUC472/mbed_overrides.c
index f2fe8303c3..2e2375bc1e 100644
--- a/targets/TARGET_NUVOTON/TARGET_NUC472/mbed_overrides.c
+++ b/targets/TARGET_NUVOTON/TARGET_NUC472/mbed_overrides.c
@@ -35,12 +35,18 @@ void mbed_sdk_init(void)
 #if MBED_CONF_TARGET_HXT_PRESENT
     /* Enable External XTAL (4~24 MHz) */
     CLK_EnableXtalRC(CLK_PWRCTL_HXTEN_Msk);
+#else
+    /* Disable External XTAL (4~24 MHz) */
+    CLK_DisableXtalRC(CLK_PWRCTL_HXTEN_Msk);
 #endif
     /* Enable LIRC */
     CLK_EnableXtalRC(CLK_PWRCTL_LIRCEN_Msk);
 #if MBED_CONF_TARGET_LXT_PRESENT
     /* Enable LXT */
     CLK_EnableXtalRC(CLK_PWRCTL_LXTEN_Msk);
+#else
+    /* Disable LXT */
+    CLK_DisableXtalRC(CLK_PWRCTL_LXTEN_Msk);
 #endif
 
 #if MBED_CONF_TARGET_HXT_PRESENT