Silicon field emitter arrays have been fabricated and investigated. Four different field emission enhancement layers were studied : (1) porous silicon layers, (2) carbon films, (3) hydrogen implanted layers, (4) Cs-enriched layers. Scanning electron microscopy was used to study the morphology of the tips. Comparison of the above arrays was accomplished by obtaining effective work functions, field enhancement factors, and effective emission areas from Fowler-Nordheim plots.