In a method of merging blocks in a semiconductor memory device according to example embodiments, a plurality of data are written into one or more first blocks using a first program method. One or more merge target blocks that are required to be merged are selected among the one or more first blocks. A merge-performing block for a block merge operation is selected among the one or more first blocks and one or more second blocks. A plurality of merge target data are written from the merge target blocks into the merge-performing block using a second program method that is different from the first program method.