Conventional directional modulation (DM) transmitters often employ phased array principles, leading to complex hardware and high power consumption. This letter presents a new method that achieves DM by utilizing the angle-sensitive property of reconfigurable intelligent surface (RIS). Based on this method, we propose a RIS-based architecture for DM transmitters that eliminates the need for conventional radio frequency (RF) chains. Through the real-world demonstration of a quadrature phase shift keying (QPSK) DM prototype system, we confirm that the proposed RIS-based DM transmitter achieves the same bit error rate (BER) performance as a conventional transmitter in the desired transmission direction. Additionally, when gradually deviating from the desired direction, the BER of the RIS-based DM transmitter deteriorates faster than that of the conventional transmitter, validating the feasibility of our proposed approach.