A multilayer planar transmission line (10) can be fabricated as a monolithic structure with series/shunt-connected components for integration in an MMIC device. The multilayer planar transmission line (10) includes a first transmission line structure (TL1) formed by a top conductor (14) and an interlevel conductor (16) separated by an interlevel dielectric (18). This structure is formed on one planar surface of a substrate (12), and a ground plane reference (20) is formed on the opposing surface, yielding second and third transmission line structures (TL2, TL3) formed by the groundplane reference and, respectively, the interlevel conductor (16) and the top conductor (14). The interlevel dielectric layer (18) is significantly thinner than the substrate dielectric, so that the first transmission line (TL1) is tightly coupled, and substantially unaffected by parasitics between the bottom of the interlevel conductor (16) and the groundplane reference (20). In an exemplary embodiment, a monolithic multilayer planar transmission line network is configured as a Marchand-type balun (30). A top conductor (34) is configured in two continuous sections (Z1 and Z2), and an interlevel conductor (36) is configured in two separate sections (ZS1) and ZS2), separated by a balance point gap (BP). This configuration forms series transmission lines (Z1 and Z2) shunt-connected to a second pair of series transmission lines (ZS1 and ZS2). With the appropriate configuration of the top and interlevel conductors (34, 36), impedance values can be established to yield a balanced signal output at the balance point gap (BP).