Apparatuses and methods for providing internal clock signals of different clock frequencies in a semiconductor device are described in the present application. An example apparatus includes a read command buffer and a read data output circuit. The read command. buffer buffers a read command responsive to a first clock signal and provides the read command responsive to a second clock signal. The read data output circuit receives a plurality of bits of data in parallel when activated by the read command from the read command buffer, and provides the plurality of bits of data serially responsive to input/output (IO) clock signals. A data clock timing circuit provides the IO clock signals having a first clock frequency in a first mode and having a second clock frequency in a second mode, and further provides the second clock signal having the first clock frequency in the first and second modes.