A data input/output circuit of a semiconductor memory device has a data inversion determination function. In an input mode, the data input/output circuit inverts an input data group in response to an input inversion flag and transmits the inverted input data group to a memory cell array. In an output mode, the data input/output circuit inverts a data group, output from the memory cell array, when the output data group satisfies a predetermined inversion condition, and transmits the inverted output data group to the outside of the data input/output circuit. In this case, an output inversion flag, indicating that the output data group is to be inverted, is generated. Further, the data input/output circuit stores the input inversion flag in the memory cell array in the input mode, and compares the input inversion flag, stored in the memory cell array, with the output inversion flag in the output mode. According to the data input/output circuit and the semiconductor memory device having the data input/output circuit, it can be readily determined whether a data inversion function is normally performed.