diff --git a/CH32V203/src/main.c b/CH32V203/src/main.c
index 8c67e46..a71a2fb 100644
--- a/CH32V203/src/main.c
+++ b/CH32V203/src/main.c
@@ -59,6 +59,7 @@ void SysTick_Handler(void)
 }
 
 
+void int_to_unicode(uint32_t value , uint8_t *pbuf , uint8_t len);
 void USB_Config(void)
 {
     NVIC_InitTypeDef NVIC_InitStructure;
@@ -67,6 +68,15 @@ void USB_Config(void)
     RCC_USBCLKConfig(RCC_USBCLKSource_PLLCLK_Div3);
     RCC_APB1PeriphClockCmd(RCC_APB1Periph_USB, ENABLE);
 
+    /* update serial number string with chip unique ID */
+    extern uint8_t USBD_StringSerial [];
+    uint32_t serial0 = *(uint32_t*)0x1FFFF7E8;
+    uint32_t serial1 = *(uint32_t*)0x1FFFF7EC;
+    uint32_t serial2 = *(uint32_t*)0x1FFFF7F0;
+
+    int_to_unicode(serial0 + serial2, &USBD_StringSerial[2],  8);
+    int_to_unicode(serial1 + serial2, &USBD_StringSerial[18], 4);
+
     USB_Init();
 
     NVIC_InitStructure.NVIC_IRQChannel = USB_LP_CAN1_RX0_IRQn;
@@ -143,3 +153,22 @@ void Delay_Ms(uint32_t n)
     for(int i = 0; i < SystemCoreClock / 4000 * n; i++) __NOP();
 }
 
+
+void int_to_unicode(uint32_t value , uint8_t *pbuf , uint8_t len)
+{
+    for(int i = 0 ; i < len ; i++)
+    {
+        if((value >> 28) < 0xA)
+        {
+            pbuf[2 * i] = (value >> 28) + '0';
+        }
+        else
+        {
+            pbuf[2 * i] = (value >> 28) + 'A' - 10;
+        }
+
+        pbuf[2 * i + 1] = 0;
+
+        value = value << 4;
+    }
+}
diff --git a/CH32V305/src/USBD/usb_desc.c b/CH32V305/src/USBD/usb_desc.c
index c519d09..e9bd4a8 100644
--- a/CH32V305/src/USBD/usb_desc.c
+++ b/CH32V305/src/USBD/usb_desc.c
@@ -402,7 +402,7 @@ const uint8_t USB_StringProduct[] =
 
 
 /* Serial Number Descriptor */
-const uint8_t USB_StringSerialNbr[] =
+uint8_t USB_StringSerialNbr[] =
 {
     USB_SIZE_STRING_SERIALNBR,
     USB_DESCR_TYP_STRING,
diff --git a/CH32V305/src/USBD/usb_desc.h b/CH32V305/src/USBD/usb_desc.h
index 0dd60c9..d6567cc 100644
--- a/CH32V305/src/USBD/usb_desc.h
+++ b/CH32V305/src/USBD/usb_desc.h
@@ -62,7 +62,7 @@ extern const uint8_t USB_CfgDesc_HS[];
 extern const uint8_t USB_StringLangID[];
 extern const uint8_t USB_StringVendor[];
 extern const uint8_t USB_StringProduct[];
-extern const uint8_t USB_StringSerialNbr[];
+extern       uint8_t USB_StringSerialNbr[];
 extern const uint8_t USB_QualifierDesc[];
 extern const uint8_t HID_ReportDesc_FS[];
 extern const uint8_t HID_ReportDesc_HS[];
diff --git a/CH32V305/src/main.c b/CH32V305/src/main.c
index c52d27a..78a68ac 100644
--- a/CH32V305/src/main.c
+++ b/CH32V305/src/main.c
@@ -11,7 +11,7 @@ volatile uint32_t SysTick_ms = 0;
 
 
 void SysTick_Config(uint32_t ticks);
-
+void int_to_unicode(uint32_t value , uint8_t *pbuf , uint8_t len);
 
 void main(void)
 {
@@ -19,6 +19,15 @@ void main(void)
 
     VCOM_Init();
 
+    /* update serial number string with chip unique ID */
+    extern uint8_t USB_StringSerialNbr[];
+    uint32_t serial0 = *(uint32_t*)0x1FFFF7E8;
+    uint32_t serial1 = *(uint32_t*)0x1FFFF7EC;
+    uint32_t serial2 = *(uint32_t*)0x1FFFF7F0;
+
+    int_to_unicode(serial0 + serial2, &USB_StringSerialNbr[2],  8);
+    int_to_unicode(serial1 + serial2, &USB_StringSerialNbr[18], 4);
+
     USBHS_RCC_Init();
     USBHS_Device_Init(ENABLE);
 
@@ -52,3 +61,23 @@ void SysTick_Handler(void)
 
     SysTick_ms++;
 }
+
+
+void int_to_unicode(uint32_t value , uint8_t *pbuf , uint8_t len)
+{
+    for(int i = 0 ; i < len ; i++)
+    {
+        if((value >> 28) < 0xA)
+        {
+            pbuf[2 * i] = (value >> 28) + '0';
+        }
+        else
+        {
+            pbuf[2 * i] = (value >> 28) + 'A' - 10;
+        }
+
+        pbuf[2 * i + 1] = 0;
+
+        value = value << 4;
+    }
+}