A ring oscillator circuit for measurement of negative bias temperature instability effect and/or positive bias temperature instability effect includes a ring oscillator having first and second rails, and an odd number (at least 3) of repeating circuit structures. Each of the repeating circuit structures in turn includes an input terminal and an output terminal; a first p-type transistor having a gate, a first drain-source terminal coupled to the first rail, and a second drain source terminal selectively coupled to the output terminal; a first n-type transistor having a gate, a first drain-source terminal coupled to the second rail, and a second drain source terminal selectively coupled to the output terminal; and repeating-circuit-structure control circuitry. The ring oscillator circuit also includes a voltage supply and control block.