Computer c = new Computer(){
     GPUEnabled = true
};

c.Open();

foreach( var hardware in c.Hardware) {
     if( hardware.HardwareType == HardwareType.GpuAti ) {
          hardware.Update();

          foreach( var sensor in hardware.Sensors ) {
              if( sensor.SensorType == SensorType.Temperature ) 
                   MessageBox.Show(sensor.Name  + ": " + sensor.Value.GetValueOrDefault());
          }
     }
}