A clock generation device and a semiconductor device including the same are disclosed, which may tune an internal clock to a desired frequency. The clock generation device may include an oscillator configured to tune an oscillation signal in response to a tuning signal, and adjust a period of an internal clock. The clock generation device may include a counter configured to count the internal clock in response to a count enable signal, and output a count signal. The clock generation device may include a comparator configured to compare the count signal with a test count signal including a target count number of the internal clock, and output the tuning signal.