A new systematic method is presented for the design of high-efficiency microwave oscillators. It is based on the control of the transistor output-voltage waveform, through the combined use of a nonperturbing auxiliary generator and a substitution generator. The nonperturbing generator sets the oscillation frequency at the desired value during the entire design process. The combination of the two generators allows obtaining a quasisquare output-voltage waveform, with optimum harmonic components to maximize the efficiency. Attention is paid to the stability and phase noise of the implemented oscillator, which are analyzed versus technological parameters. A 6-GHz oscillator has been designed using these techniques, with good experimental results.