Formation mechanisms of self-organized Si-needles generated by anodic etching of lowly doped p-type silicon wafers in an aqueous HF solution in the transition region (region between the pore formation and the electropolishing) is studied through surface SEM images taken after different etch times. Impacts of current density, substrate resistivity range in the lowly doped region, and electrolyte additives on morphology of needles are also investigated. A simple model based on pore formation models is presented to describe formation of self-organized needles during anodic etching of lowly doped p-type silicon in an aqueous HF solution in the transition region. The validity of the model is discussed by comparison to experimental results. (C) The Author(s) 2018. Published by ECS.