The bilayer microbeam can be assigned with two different thermal expansion coefficients, so that the microbeam can be used as a thermal actuator, which can provide bending with thermal loading. As a microdevice, the size effect plays an important role. In addition, the length height ratio L/h of the microbeam has to be smaller than 20, to provide sufficient support. With this ratio, the shear effect of the beam can not be ignored. In this work, considering both the size and shear effects, we modified the couple stress and Timoshenko beam theories to study the thermal bending of bilayer microbeams. By using the principle of minimum potential energy, we derived the higher-order governing equations under thermal load. Then with specified boundary conditions, we adopted the differential quadrature method to solve the governing equations. Finally, using a bilayer microbeam made of aluminum and polysilicon as an example, we verified effects of transverse shear and beam size. Results show that the size effect on beam stiffness is significant when the beam height is on the order of equivalent length scale (leq). Moreover, considering the transverse shear effect indicates that the lateral deflection of the Timoshenko beam depends on the ratio L/h: as L/h increases, the tip deflection increases and converges to the classical solution. Specifically, for a Timoshenko beam with h/leq = 15, the change in deflection can reach 44.6% when L/h is increased from 5 to 25.