Method of detecting touch position

A method of determining a touch position is provided to determine a correct touch position of a touch panel to improve the reliability of a touch panel display device including the touch panel. A touch panel includes first signal lines(GLmin,GLn-1,GLn) arranged in a first direction, second signal lines(DLmin,DLm-1,DLm) arranged in a second direction perpendicular to the first direction, and photo-sensing elements respectively disposed at intersections of the first signal lines and the second signal lines. The photo-sensing elements sense external light and output sensor data. The number of photo-sensing elements which output sensor data having gray scales of greater than a threshold value is counted along the first and second signal lines. The point, at which the first signal line having the minimum counted number of photo-sensing elements and the second signal line having the minimum counted number of photo-sensing elements intersects each other, is determined as a touch position of the touch panel.