To reduce the molecular diffusion mixing time in a microreactor, the efficacy of a layered flow pattern generated by an alternate pumping system has been reported. In this paper, we propose an asterisk-shaped channel, which has two inlets and two diverging mixing channels, for the enhancement of mixing using the layered structure flow pattern. Using scaled-up models, the characteristics of the flow pattern in the asterisk-shaped channel was investigated in association with the pumping condition and the channel geometry. Because the gap between the inlets is small in the asterisk-shaped channel, a layered structure is generated under easy pumping condition, which could be practicable. The layer thickness in the diverging channel becomes smaller downstream, so the diverging channels reduce the molecular diffusion time that is proportional to the square of the mixing length, i.e. the layer thickness in this case. For instance, in the case that the width and length of the mixing channel are 5 times and 20 times of the inlet width, the mixing time in the asterisk channel with alternate pumping could be reduced to two orders of magnitude smaller than that in an ordinary microreactor.