// referans olarak System.Management ekle
// namespace'i projemize dahil ediyoruz using System.Management;
// method olarak veya istediğiniz event'a ekleyiniz ör: click event

ManagementObjectSearcher theSearcher = new ManagementObjectSearcher("SELECT * FROM Win32_DiskDrive WHERE InterfaceType='USB'");
foreach (ManagementObject currentObject in theSearcher.Get())
{
ManagementObject theSerialNumberObjectQuery = new ManagementObject("Win32_PhysicalMedia.Tag='" + currentObject["DeviceID"] + "'");
MessageBox.Show(theSerialNumberObjectQuery["SerialNumber"].ToString());
}