This study is intended to be the starting point for theory of branching channels that supply reactants into chemical microreactors positioned on the surface of a microchip. The channels are assumed to be made by isotropic etching - and therefore of the same depths everywhere, irrespective of their cross-section area. When required to handle larger flows, the channels are therefore wide and thus occupy a substantial proportion of the available surface area. Because of the intended starting-point character, this discussion of the branchings assumes the simplest, isokinetic bifurcation. The branching pattern may resemble the self-similar pattern of fractal objects, but the constant depth makes the fractal theory inadequate. The evaluation of the chip surface areas occupied by the three basic components of the system - the reactors, the sealing strips, and the channels - uses a two-parametric model, with widths of the channels and sealing strips as the independent variables. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.