In this thesis, we added the thermochromic materials into the pcW-LED to solve the blue light leakage during the pcW-LED aging process. The thermochromic materials could change their color and absorb the leaking blue light immediately when the temperature of the phosphor was too high. Furthermore, to begin with, we measured and analyzed several different materials in the experiment. Also, we predicted the temperature distribution inside the LED by applying thermal simulation in order to find the best location and shapes of the materials. Finally, we compared the result of the LED which thermochromic materials was applied with the LED without thermochromic materials to see if there were significantly different.