An RF SOI switch includes patterned or self-aligned low-k features (i.e., low-k polymer structures or voids) in the PMD and/or subsequently formed inter-metal dielectric layers to reduce capacitive coupling. All portions of the dielectric layers through which metal contact/via structures pass are pre-designated as reserved regions, and formation of the low-k features is restricted to interstitial regions located between adjacent reserved regions. After the low-k features are formed, dielectric material is deposited into all reserved regions, and then the metal contact/via structures are formed according to standard practices through the dielectric material disposed in the reserved regions. The low-k features are formed by polymer material sandwiched between two passivation layers. Optional openings are formed through the upper passivation layer, and then the polymer material is asked out to generate void-type features. Optionally, polymer is spin-coated over the metal line structures, then etched back to form self-aligned low-k features.