Porous silicon (PS) with a micro-nano-hybrid structure has been successfully fabricated with an electrochemical etching process. The micropores consist of one-dimensional tunnels, which vary from ca. 1 to 1.5 mu m in pore diameter and extend up to 15 mu m in depth. The walls of these micropores are covered with a nanoporous structure that consists of small spherical particles, the feature size of which is of the order of tens of nanometers or smaller. The as-prepared PS structures show cathodic/anodic peaks for lithiation/delithiation during cyclic voltammetry with minimal destruction of either the micropore or nanopore of its wall even after 50 cycles. Furthermore, the peak current, the cumulative charge increase, and the electrochemical impedance for electrode reactions consistently decreases with the surface area of the tunnel wall, indicating that processes at the tunnel wall govern the overall lithiation/delithiation reactions. A hybrid porous structure consisting of microtunnels with nanostructured surface layers appears to provide a viable and practical way to utilize silicon for anode materials in rechargeable microbatteries. (c) 2008 The Electrochmical Society.