An exemplary illumination device includes an enclosure, a semiconductor light source accommodated in the enclosure, and an envelope engaged with the enclosure and covering the semiconductor light source. Light generated by the semiconductor light source can project through the envelope and out of the illumination device. The semiconductor light source includes a plurality of light source modules independent from each other. A plurality of air passages are defined in each light source module for air passing therethrough to dissipate heat generated by the semiconductor light source into ambient air.