The present invention is to provide a semiconductor device capable of searching for a block with a minimum erasure count at a high speed and a method of searching for an erasure count in a semiconductor memory. In response to a search start instruction, a read address signal including address sequences for blocks is generated and the read address signal is provided to a block management memory to successively read sequences of erasure count data pieces corresponding to the blocks from the block management memory. Thereafter, when the erasure count data piece read from the block management memory represents an erasure count smaller than a minimum erasure count data piece, the erasure count data piece is imported and retained and outputted as the minimum erasure count data piece. Also, the read address signal is imported and retained and an address indicated by the read address signal is outputted as a minimum erasure count address.