A method of detecting an error of a multi-time programmable (MTP) operation in which each gamma-offset and each header-bit at predetermined reference gray-levels are written in a MTP memory device while the MTP operation is performed on a pixel circuit, the each header-bit indicating whether or not the each gamma-offset is written in the MTP memory device, and it is detected whether or not the MTP operation is performed on the pixel circuit based on a logical operation between the header-bits at the predetermined reference gray-levels read from the MTP memory device when the MTP operation is finished on the pixel circuit.