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The development of a novel vacuum differential amplifier (diff-amp) array employing vertically configured nanodiamond (ND) vacuum field emission transistors (ND-VFETs) on a single chip is presented. The diff-amp array is composed of a common ND emitter array integrated with partition gates and split anodes. An identical pair of ND-VFETs with well-matched field emission transistor characteristics was fabricated by using a dual-mask well-controlled microfabrication process, involving a mold-transfer self-aligned gate-emitter technique in conjunction with ND deposition into the micropatterned molds in the active layer of a silicon-on-insulator substrate followed by gate partitioning to form diff-amp array. The ND-VFETs show gate-controlled modulation of emission with distinct cutoff, linear, and saturation regions. Signal amplification characteristics of the ND-VFET diff-amp are presented. A large common-mode-rejection ratio (CMRR) of 54.6 dB was measured for the diff-amp. The variation of CMRR performance with transconductance was examined, and the results were found to agree with the equivalent circuit model analysis. The accomplishment of this basic circuit building block, consisting of an integrated diff-amp, demonstrates the feasibility of using vacuum integrated circuits for practical applications, including high-radiation and temperature-tolerant space electronics.