Clock generation and control in a semiconductor system having process, voltage and temperature (PVT) variation. A semiconductor device may include at least first and second ring oscillators, each disposed at locations respectively closest to first and second logic circuits of an operation circuit, and generating first and second oscillating signals. A detecting circuit is configured to perform a predetermined logic operation on the first oscillating signal and the second oscillating signal to generate a first clock signal. A calibration circuit is configured to receive the first clock signal from the detecting circuit and perform a delay control on each of the first ring oscillator and the second ring oscillator to generate a second clock signal for operating the operation circuit.