An on-chip clock controller includes a clock-control chain configured to shift first clock-control bits in serial and output the first clock-control bits to a first clock domain in parallel in response to a clock-control scan clock provided from outside of a chip, and a first domain clock generator, the first domain clock generator configured, during a test mode, to generate a first internal clock by selectively outputting a first data scan clock provided from outside of the chip or a first functional clock generated from inside of the chip.