A linear piecewise model has been formulated to analyze the performance of a metallic microheater integrated with single-mode waveguides (λ ∼ 1550 nm) in silicon-on-insulator (SOI). The model has been used to evaluate integrated optical microheaters fabricated in a SOI substrate with 2 μm device layer thickness. The Fabry-Perot modulation technique has been used to extract the effective thermo-optic phase shift and response time. The effective thermal power budget of Peff,π ∼ 500 μW(out of actually consumed power Pπ = 1.1 mW) for a π phase shift and a switching time of τ ∼ 9 μs, have been recorded for a typical Ti heater stripe of length LH = 50 μm, width WH = 2 μm, and thickness tH ∼ 150 nm, integrated with a FabrÿCPerot waveguide cavity of length ∼20 mm. It has been shown that the performance of a heater improves (in terms of power budget) as the length of a microheater decreases. However, smaller heater size requires higher joule heating to obtain a desired phase shift, which is again found to be dependent on polarization of the guided mode because of thermal stress. © 2016 Optical Society of America.