This paper reports in situ quantitative studies of wear under electric excitation in polysilicon micromotors. Two polysilicon variable-capacitance rotary side-drive micromotor types, including harmonic and salient-pole, are described. Voltages as low as 26 and 35 V across 1.5-micron gaps are sufficient for operating the harmonic and salient-pole side-drive micromotors, respectively. Extended operation of the harmonic micromotors to near 100 million wobble cycles are studied at excitation frequencies of 10,000 and 25,000 r/min for operational durations of 150 and 71 h, respectively. The results indicate that, with micromotor operation, the rotor inner radius asperities wear out and the bearing clearance increases. This bearing wear is significant and results in changes in the gear ratio of the harmonic micromotors by as much as 22 percent. Typical gear ratios are near 90 at the start of harmonic micromotor operation and decrease to near 70 as the bearings wear out. For the salient-pole micromotors, wear particles are observed to form in the bearing and at the bushings. These wear particles are adhered to the bushing surfaces and the area near the edge of the rotor inner radius.