A semiconductor memory device utilizing a data coding method in an initial operation. The semiconductor memory device includes a plurality of counters communicating with a data coding unit. The counters count the number of data bits and flag information data bits in a first logic state in a first data group which includes at least one data bit and second through nth groups each including at least one data bit and flag information. The data coding unit selectively applies a first operation mode and a second operation mode to each of the first through nth data groups and codes the data of each of the first through nth data groups. The first operation mode codes the data of each of the first through nth data groups such that the counted number of data bits in the first logic state in each of the first through nth groups is minimized. The second operation mode codes the data of each of the first through nth groups such that the difference between the number of data bits and flag information data bits in the first logic state and the number of data bits and flag information data bits in a second logic state in the first through nth data groups is minimized. In this manner, the semiconductor memory device and the associated data coding method prevents the initial logic state of data from being changed due to a voltage drop in the initial operation of the device.