The present invention relates to a digital television (DTV) transmitter/receiver. In the DTV transmitter, enhanced data is pre-processed by coding the enhanced data for forward error correction (FEC) and expanding the FEC-coded enhanced data. Enhanced data packets are generated including the pre-processed enhanced data and known data is inserted to at least one of the enhanced data packets. The enhanced data packets are multiplexed main data packets including main data. An RS encoder RS-codes the multiplexed main and enhanced data packets, the RS encoder adding systematic parity data to each main data packet and adding RS parity place holders to each enhanced data packet. The RS encoder may also insert non-systematic RS parity data or null data into the RS parity place holders included in each enhanced data packet.