Unveiling the nature of dark matter (DM) is one of the fundamental open questions in Physics today. A big-bang relic population of Weakly Interacting Massive Particles (WIMPs) is among the most favoured candidates. Earth-based direct detection experiments aim to detect the low-energy recoils induced by WIMP-nucleus scattering in an instrumented target. Searching for WIMPs down to neutrino floor is among the highest priorities of the astroparticle physics community for the next decade, but no evidence of this process has been unambiguously reported so far. <br/>The null results of current searches for a DM particle at the electroweak scale may be interpreted as a need for a change of paradigm. There is increasing interest in alternative models for DM, and a rich phenomenology, most notably at low masses (<10 GeV/c2). DarkSide-20k will be the first experiment to use novel and specialised ultra-low background silicon photosensors to read out a 50 t liquid argon target, searching for WIMPs. This proposal aims to exploit the potential of the SiPM technology developed for DarkSide-20k to broaden the sensitivity to low-mass DM candidates, by searching for dark matter interactions in the silicon sensors themselves.<br/><br/>The goal of the Si4DM (Silicon for Direct Detection of DM in Darkside) project is a world-leading DM search in a novel detector reaching beyond the WIMP paradigm. The proposal objectives are: <br/>- the background rejection and energy measurement characterisation in the novel SiPMs, to enable an event-by-event search for DM interactions in the Si, with electron final states; and <br/>- to develop the first search for DM in a SiPM target, using sidereal modulation.