A proposed simply structured gated silicon (Si) drift X-ray detector operated using Peltier cooling and only a single high-voltage source is investigated. Because the device structure is much simpler than that of commercial Si drift detectors (SDDs), which require at least two high-voltage sources, the cost of the X-ray detection system can be reduced. The absorption of cadmium X-ray fluorescence photons (energy: 23.1 keV) in 0.3-mm-thick Si is only 19% in commercial SDDs. Toward realizing detectors with thicker Si substrates, we simulate the electric potential distribution in the proposed detector with a Si substrate having thickness of 0.625 mm and resistivity of 10 kΩ·cm, and we perform fundamental experiments on a fabricated prototype. The simulation result is in good agreement with the experimental result that the effective active area of the detector is approximately 18 mm2 by using incident X-rays passed through a 0.1-mm-diameter pinhole. An energy resolution of 145 eV at 5.9 keV is experimentally obtained from an 55Fe source at -38 °C.