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This paper reports a micromachined recuperative heat exchanger integrated with in-situ temperature sensors. In this design, numerous high-conductivity silicon plates, integrated with platinum resistance temperature detectors (Pt RTDs) are fabricated and stacked alternating with low- conductivity Pyrex spacers. The device is intended for use with Joule-Thomson (J-T) coolers. The fabricated versions of the device have a footprint of 1 x 1 cm2, and lengths of up to 2 cm. Tests at cryogenic temperatures (120-210 K) show that the effectiveness of the heat exchanger is as high as 0.785. In a preliminary J-T self-cooling test, the temperature at the expansion orifice dropped 13 K from the inlet temperature for an inlet pressure of 527 kPa (76 psia). The integrated Pt RTDs presented a sensitivity of 0.26%/K in the linear operational range of 150-300 K, but remained usable at temperatures below that range. Details regarding evaluation apparatus are discussed.