The Silicon Electron Multiplier (SiEM) sensor is a novel sensor concept that enables charge multiplication by high electric fields generated by embedded metal electrodes within the sensor bulk. Metal assisted chemical etching (MacEtch) in gas phase with platinum as a catalyst has been used to fabricate test structures consisting of vertically aligned silicon pillars and strips on top of a silicon bulk. The pillars are around 10 µm in height with a diameter of 1.0 µm and are arranged as a hexagonal lattice with a pitch of 1.5 µm. Electrical characterisations through current–voltage measurements inside a scanning electron microscope and a climate chamber have demonstrated that the MacEtch process is compatible with p–n junctions.