Ko repeated her first-round effort by hitting a four-under 67, to be eight-under overall.
The 17-year-old managed five birdies, with her only bogey coming on the par-four fourth hole.
Ko is tied at eight-under with South African Lee-Ann Pace. American Laura Diaz leads the field at 11-under.
Meanwhile, Steven Alker has continued his good form at the Web.com Tour's Boise Open by shooting a second-round five-under 66.
Alker went into the clubhouse in second place one shot behind leader Bill Lunde, although several players have yet to finish their rounds.