Intel rose from 42.2 percent in May to 51.2 percent in June in the US retail market.
Meanwhile, the percentage of PCs running processors from Advanced Micro Devices declined from 57.4 percent in May to 48.5 percent in June.
The shift came because of an emphasis on inexpensive notebooks containing Celeron M chips, according to Sam Bhavnani, director of research at Current Analysis. In notebooks, Intel expanded its market share from 57.3 percent in May to 66.2 percent in June. AMD's notebook share dropped from 42.3 percent in May to 33.4 percent in June.