Semiconductor FET devices with bottom dielectric isolation and high-κ first are provided. In one aspect, a semiconductor FET device includes: a substrate; at least one device stack including active layers oriented horizontally one on top of another on the substrate; source and drains alongside the active layers; and gates, offset from the source and drains by inner spacers, surrounding a portion of each of the active layers, wherein the gates include a gate dielectric that wraps around the active layers but is absent from sidewalls of the inner spacers. A method of forming a semiconductor FET device is also provided.