This paper describes a fully integrated 2.4-GHz 0.5-W high efficiency class-E voltage controlled oscillator (VCO) in 0.15-m GaAs pseudomorphic high-electron mobility transistor (PHEMT) process. The proposed power VCO is based on a class-E topology with a π-feedback network. The proposed class-E power VCO achieves an output power of 27 dBm with an efficiency of 42.5%, when the dc supply voltage is 6 V with a current consumption of 196 mA. The phase noise is 118.33 dBc/Hz at 1-MHz offset. The frequency tuning range with various dc supply voltage is from 2.29 to 2.45 GHz. The chip size of the class-E power VCO is 2×2 mm 2. This work has the highest efficiency among the reported fully integrated power oscillators using HEMT technologies.