This paper reports self-sustained motion of a low frequency MEMS resonator that leans on tiny p-type silicon piezoresistive nanowires, as a result of Thermal Piezoresistive Back Action (TPBA). In this device, a velocity dependent force arises from physical coupling between mechanics and electronic transport in small conductive silicon beams because of self-heating. Up to date, only damping rate increase has been reported for p-doped silicon beams based MEMS resonators. So far, most papers required n-doped silicon beams to allow self-sustained oscillation. Yet, this paper demonstrates self-sustained motion using p-doped silicon nanobeams as TPBA actuators under a constant bias voltage. The quality factor (QF) of the resonator increases from 28000 under vacuum to at least 1.8×106 for DC-bias voltage down to 950 mV. Self-oscillation is observed for bias voltage at 1,11 V. TPBA modeling accounts for the experimental results and attributes a major contribution for the amplification efficiency to the nanobeams thermal time constant along with the nanoscale size effects. © 2017 IEEE.