Since the power consumption of data centers keeps increasing, a 48-V rack power distribution system replaces the conventional 12-V power bus to reduce the power delivery IR losses. Meanwhile, the 48 V needs conversion into 1 V or lower at the point-of-load for microprocessors. A 48V-to-12V DC-DC converter can serve as a first stage between the huge gap of 48V-to-1V, in a two-stage voltage regulator module (VRM). Thus, this paper presents a 3-phase resonant switched-capacitor (<inline-formula> <tex-math notation="LaTeX">3\Phi </tex-math></inline-formula>-ReSC) converter as the first stage of the VRM. Different from the reported solutions, 3-phase resonant operation reduces the current stress across each small-size GaN switch, and thus improves the power conversion efficiency. In addition, we also present the theoretical analysis and design procedures for the <inline-formula> <tex-math notation="LaTeX">3\Phi </tex-math></inline-formula>-ReSC converter. We demonstrated the proposed <inline-formula> <tex-math notation="LaTeX">3\Phi </tex-math></inline-formula>-ReSC converter with a 98% peak power efficiency at an output current of about 1 A, with a maximum output current of 10 A.