Asustek Computer's ZenFone 5 smartphone has been the top-selling model in Japan's SIM-free segment for the fifth consecutive month since its debut in the market in November 2014, according to data compiled by Japan-based market research firm BCN.

However, the differences of market share among the top-five vendors in the SIM-free smartphone segment have been narrowed significantly, with Asustek seeing its share drop to 24.5% in March 2015, form 43% in Novmber 2014, BCN said.

LG Electronics took second place in March with a 19.5% share, buoyed by the launch of Nexus 5.