This paper presents a new ceramic package for high-frequency MMIC modules. The package is formed from a multilayer ceramic frame whose layers are metallized over most of both sides and co-fired. The inside and outside of the frame are metallized, except around the RF and DC terminals. This new package structure can eliminate ring resonances that occur in conventional ceramic packages and can provide high I/O isolation over a wide frequency range. The RF terminal is formed from microstrip lines and a through-wall microstrip designed to have a 50-ohm impedance. The insertion loss of each RF terminal is less than 0.5 dB up to 33 GHz, with complementary I/O isolation in excess of 30 dB. The new package also provides the low input V.S.W.R. of 1.3 : 1. A 30-GHz-band MMIC module incorporating four GaAs MMIC amplifiers is demonstrated. This module's maximum gain is 19 dB, and its input V.S.W.R. is 1.5 : 1 from 30.5 to 32.5 GHz.