Provided is an avalanche photodetector with an integrated micro lens. The avalanche photodetector includes a light absorbing layer on a semiconductor substrate, an amplification layer on the light absorbing layer, a diffusion layer within the amplification layer, and the micro lens disposed corresponding to the diffusion layer. The micro lens includes a first refractive layer and a second refractive layer having a refractive index less than that of the first refractive layer.