Determination of one or more operating conditions (leakage current, temperature and/or workload) of a functional transistor in a semiconductor integrated circuit (IC). The functional transistor provides an electrical current, which is provided as an input to a ring oscillator (ROSC). The ROSC is located in the IC proximate to the functional transistor and has an oscillation frequency in operation. The one or more operating conditions of the functional transistor are determined based on the oscillation frequency of the ROSC.