In a 2D electron gas with Rashba spin-orbit coupling H = ℏ²k²/2m + λ(k×σ)·ẑ, the Berry curvature of the split bands gives an intrinsic spin Hall conductivity σ_SH = e/8π (in 2D). This contribution is purely geometric — requiring no impurities — and is a hallmark of topological band physics.