Bulk-acoustic-wave piezoelectric thin-film technology has been used to synthesize delay lines at microwave frequencies in semiconductor substrates. These structures use either ZnO or AlN for piezoelectric transduction, suitably positioned electrodes for applying an AC signal, and reflecting surfaces for guiding the acoustic energy. The delay lines are accessed entirely from the top side of the semiconductor wafer. These delay structures can be incorporated as the feedback element in an oscillator and the 2 pi periodicity in these structures exploited to obtain a comb generator output. The results of delay-line oscillators operating near 1 GHz and 3 MHz spectral line spacing are reported. Noise performance exceeds -90 dBc/Hz at 1 kHz. Design and analysis is based on the use of SPICE 2G linear circuit models. Because the transducer fabrication process uses semiconductor processing technology as its basis, the synthesis of these oscillators is being studied as an integrable alternative to other technologies.