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A wafer-bonded silicon power transistor has been shown to function as an x-ray detector. The device consists of two thin device wafers bonded onto either side of a 2 mm-thick high-resistivity silicon wafer. The hydrophobic bonding process was performed at 400deg C. This low temperature wafer bonding technique should enable the development of large-area, position-sensitive detectors, using thick, high-resistivity intrinsic silicon bonded to thin readout wafers fabricated using conventional CMOS technology. These devices should enable fabrication of thicker intrinsic silicon detectors than currently available. Thick, position-sensitive detectors based on double-sided strip detectors and pixellated detectors are possible. To demonstrate this, a 1 mm thick gamma-ray detector was created from two 0.5 mm thick wafers that were patterned with gamma-ray strip detectors. The energy resolution of the detector is 8.9 keV FWHM for 60 keV gamma rays at room temperature with a leakage of 0.9 nA while operating at 700 V and fully depleted. Improvements in the technique should allow for thicker detectors with better energy resolution.