Born in Lichtenvoorde, Oost Gelre, Gelderland, Boschker made his professional debuts with FC Twente in the 1989–90 season, appearing in one game with the first team.

[citation needed] Aged almost 33 Boschker moved to AFC Ajax, but had to settle with battling for being backup with the Amsterdam club, unable to dislodge youth product Maarten Stekelenburg.

The following summer he returned to Twente, adding next to 200 more official appearances (in the 2008–09 campaign, he only missed five league contests for an eventual runner-up finish), and playing into his 40s.

[citation needed] In 2009–10, Boschker played in all 34 games as Twente won the first league title in the club's history – he only conceded 23 goals, second-best in the competition.

[citation needed] Although Boschker never made an appearance for the Netherlands until 2010, he was included in Marco van Basten's provisional squad for UEFA Euro 2008.