To reduce the power dissipation of the receiver in accordance with the intensity of the received signal, we developed the first intra-symbol intermittent (ISI) radio-frequency (RF) front end with 0.35-µm CMOS technology. In the demodulation mechanism, the RF output of the low-noise amplifier (LNA) is down-converted to an intermediate frequency (IF) by the mixer, and the LNA and mixer operate synchronously and intermittently within the length of a single symbol. Because the time-averaged power consumption is proportional to the operating time, the demodulation can be performed with low power by making the total operating time short. We experimentally demonstrate that demodulation (BPSK: 9.6kbps) is properly achieved with the operating-time ratio of 12%. This ISI operation of the RF front end is enabled by a newly devised fast-transition LNA and mixer. A theoretical analysis of aliasing noise reveals that RF ISI operation is more useful than current-control with continuous operation and that an operating-time ratio of 10% is optimal.