Just over 14 million tuned in for the opening 90 minutes of the semi-final, 16.484 million for extra time and 18.141 million for the 12 minutes and 32 seconds of penalties, Barlovento said in a statement on Thursday, citing data from Kantar Media.
The figures refer to the average audience for transmissions of five minutes or longer and the high point in terms of total viewers was 19.086 million, coinciding with Cesc Fabregas's winning spot kick just before 11.30 p.m. local time.
Spain won the penalty shootout 4-2 after the match had ended goalless after extra time.
The rights to broadcast Euro 2012 in Spain are held by Telecinco, part of former Italian Prime Minister Silvio Berlusconi's Mediaset group.
Holders Spain will play the winners of Thursday's second semi-final between Germany and Italy in Sunday's final in Kiev.
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