A relaxation oscillator and a method for offset cancellation in a relaxation oscillator. The relaxation oscillator comprises two comparator units, each comparator unit comprising a comparator element and a memory element; and a switch control generator coupled to each of the comparator units; wherein each comparator unit, in a reset state, stores an input-offset voltage on the memory element under the control of the switch control generator such that, in a comparison state, the input-offset voltage is applied to both inputs of the comparator for implementing an offset-free threshold.