Provided are a semiconductor device including an error correction code circuit and a driving method thereof. The semiconductor device includes a plurality of normal mats including a plurality of memory cells and connected to data lines, a plurality of dummy mats arranged in specific areas of the plurality of normal mats and inputting/outputting parity bits through parity lines of a specific circuit, a plurality of free ECC (Error Correction Code) calculation circuits that perform ECC calculation corresponding to data applied through the data lines and the parity lines, and a main ECC calculation circuit that combines data applied from the plurality of free ECC calculation circuits with one another and performs ECC calculation.