With the text selected, go up to the Select menu at the top of the screen and choose Save Selection. When the Save Selection dialog box appears, just click OK. There's no need to name it or make any changes to the options.
Once you've saved your selection, press Ctrl+D (Win) / Command+D (Mac) to deselect your text.
Switch over to your Channels palette for a moment (it's grouped in beside the Layers palette) and you'll see your selection saved as a new channel named "Alpha 1" at the very bottom. We'll be coming back here a bit later to load our selection again: