Hydrogenated amorphous silicon (a-Si:H) has recently emerged as a promising material to provide microchips with passive and active photonic functions through a back-end and CMOS-compatible technological process. In this paper, we discuss the performance achieved with different configurations of a-Si:H-based electro-optical amplitude modulators integrated into passive waveguides. All of the analysed devices are based on the plasma dispersion effect, a phenomenon that allows us to reach useful performance at the communication wavelength of λ ∼ 1.55 μ m. The behaviour of the various proposed modulation approaches has been tested by ad hoc interferometric structures, such as Fabry–Perot integrated resonators or integrated Mach–Zehnder interferometer, as well as by multistack devices to enhance the static modulation efficiency. The performance of each modulator has been analysed through several figures of merit.