The goalless Iberian derby began and ended brightly, but was full of largely stalemate football for extended spells in between.
The spot-kick outcome effectively came down to who had more luck with the woodwork and the world and European champions prevailed.
With Spain leading 3-2 in the shootout, Portugal's Bruno Alves saw his penalty bounce away after striking the bar and Spain's Cesc Fabregas sent his side through when his shot went in off the post.
"We had loads of luck in the penalties," Del Bosque told a news conference. "But I want to express my congratulations to the Portuguese side because they played a great tournament, but we were luckier, we really had all the luck this time."
He also said Portugal played well overall, defended better than Spain for periods and looked dangerous in attack, but that his substitutions - bringing on Jesus Navas and Pedro for David Silva and Xavi - changed the outcome.
"We created more when they came on, we caused them more problems and it was vital I brought them on. We were looking tired and we needed the extra pace, especially in extra time when Pedro came on," he said.
"Extra time though proved our players are gaining in experience. They had the mental strength, they could deal with it."
Del Bosque said he had no difficulty finding players to take the penalties with Xabi Alonso - who missed - Andres Iniesta, Gerard Pique, Sergio Ramos and Fabregas all keen.
"There was no problem, Cesc told me he wanted take the fifth one to score the winning penalty and he did," he added.
The coach was not worried or particularly bothered who Spain would meet in Sunday's final in Kiev. Their opponents will be known after Italy play Germany in the second semi-final in Warsaw on Thursday.
"That will be a great game, and whoever we play, we play. I don't mind. Whoever we face in the final, will be a very tough opponent," he said.
Spain drew 1-1 with Italy in their opening group game.
