An oscillator circuit has a first and a second piezoresistive resonator (1,2), each having a resonant frequency, each piezoresistive resonator having an input for driving the resonator, and each piezoresistive resonator having its input coupled directly to an output of the other of the resonators, to provide feedback according to a resistance of the respective resonator without amplification and without a phase shifter. This enables feedback without the need for another component to provide the phase shift. This means a simpler circuit can be used, which can facilitate greater integration and hence lower costs. By using piezoresistive resonators the need for an external crystal can be avoided, enabling greater integration and lower costs.