A photoresist composition includes about 100 parts by weight of resin mixture including novolak resin and acryl resin and about 10 parts to about 50 parts by weight of naphthoquinone diazosulfonic acid ester. A weight-average molecular weight of the novolak resin is no less than about 30,000. A weight-average molecular weight of the acryl resin is no less than about 20,000. The acryl resin makes up about 1% to about 15% of the total weight of the resin mixture. When a photoresist film formed using the photoresist composition is heated, a profile variation of the photoresist composition is relatively small. Therefore, a residual photoresist film has a uniform thickness, and a short circuit and/or an open defect in a TFT substrate may be reduced.