Hook capped another top display with a late drop goal after booting four penalties and converting Sonny Parker's first half try. Lee Byrne also went over early in the second half to send the Ospreys on their way to the Twickenham final on April 15th.
Their joy came at the expense of Cardiff Blues who were made to pay the price for three yellow cards in the first half. Ben Blair saved their blushes on the scoreboard with a late try and conversion but it was a bitterly disappointing evening for the Cardiff region.
Scott Morgan was first in the bin after twenty-one minutes for an infringement at a ruck that allowed Hook to match Blair's early penalty. Hook and Andrew Bishop then combined to send Parker cruising through on twenty-seven minutes as the Ospreys drew first blood.
Blues lock Deiniol Jones saw a yellow card for a dangerous tackle and second row partner Robert Sidoli followed moments later following a dust up with Brent Cockbain in a full blooded Welsh derby.
Byrne slid over on forty-five minutes before Hook kicked a hat trick of penalties to give the Ospreys a commanding 24-3 lead. Blair struck back late on but Hook had the last word, his drop goal putting the icing on a top display from the Ospreys.
In the other semi-final Leicester Tigers kept Sale Sharks at arm's length for the majority of the match running out as eventual 29-19 winners over their Guinness Premiership rivals.
EDF Energy Cup Semi-Final 2
Cardiff Blues 10 - 27 Ospreys
Blues: (3) 10
Ospreys: (10) 27
Tries: Parker, Byrne
Pens: Hook (4)