[Truncated abstract] Porous silicon (PS), which exhibits valuable characteristics including photoluminescence, easily tunable refractive index, and large surface area, has gained enormous attention worldwide for innovative photoelectronic applications, such as light-emitting diodes, photodetectors, and sensors. However, only rudimentary PS optical devices and sensors exist at the present stage, due to the environmental and chemical instability of PS. For the next generation of PS devices, patterning of PS after its formation using CMOS-compatible processes to achieve PS devices with homogenous properties, and integration with electronics is desired. In this work, a low-temperature annealing technique is investigated for passivation of PS to achieve environmental and chemical stability. The low-temperature annealed PS (LTA-PS) was obtained by annealing as-fabricated PS in a rapid thermal processor at temperatures as low as 600°C under nitrogen flow. After passivation a very thin layer of SiOxNy was formed on the pore surface, acting as a protective layer against chemical attack and a diffusion barrier against further oxidation. Immersion in HF solution removed the SiOxNy passivation layer, leading to only a 2 % porosity increase. The PS surface is re-terminated with Si-H bonds after HF immersion, enabling it to be reanodised or re-passivated. Compared to as-fabricated PS, LTA-PS has significantly enhanced environmental and chemical stability. It can survive in 1 % KOH (this is a common concentration for alkaline developers in photolithography) for 100 s with an optical thickness change of less than 10 %. The annealing temperature, annealing duration and N2 flow rate were all found to influence the passivation properties. By optimising these conditions, PS annealed at 600°C for 48 minutes with a N2 flow rate of 1000 sccm exhibited excellent chemical resistance to 1 % KOH for at least 10 minutes with negligible film degradation. As LTA-PS is chemically resistant, the compatibility of LTA-PS to photolithography was investigated. It was found that the photoresist seeped into the pores, and could not be completely removed during development. A polymer protective layer (ProLIFT) was used prior to the coating of photoresist to prevent photoresist seepage and enable clean development. By use of the polymer protective layer, the LTA-PS exhibited excellent compatibility with photolithographic processes using alkaline developers. Once photolithographic process can be used with LTA-PS, both additive and subtractive processes can be employed to pattern PS. Metal deposition and definition on a PS surface was successfully achieved and demonstrated as an example of additive processes. As an example of subtractive processes, dry etching of PS was investigated in detail to find the optimum recipe for etching PS. A recipe using CF4/CH4 was selected for achieving near-90° sidewalls with a smooth post-etching surface...