Every instance of the word "essence" used by Heidegger in The Question Concerning Technology and its immediate context is listed here in chronological order.
Extract of the essay containing the word "essence"
...The relationship will be free if it opens our human existence to the essence of technology...
...can respond to this essence, we shall be able to experience the technological within its own bounds...
...Technology is not equivalent to the essence of technology...
...the essence of "tree", we have to become aware that That which pervades every tree...
...the essence of technology is by no means anything technological...
...we shall never experience our relationship to the essence of technology so long as...
... today we particularly like to do homage, makes us utterly blind to the essence of technology...
...According to ancient doctrine, the essence of a thing is considered to be what the thing is...
...this fixing by no means needs to uncover the thing in question in its essence...
...Only the true brings us into a free relationship with that which concerns us from out of its essence...
...the correct instrumental definition of technology still does not show us technology's essence...
...so that it now is the name for the essence of causality thought as the Greeks thought it...
...What has the essence of technology to do with revealing...
...then another whole realm for the essence of technology will open itself up to us...
...Of what essence is modern technology that it happens to think of putting exact science to use...
...a water power supplier, derives from out of the essence of the power station...
...the machine is not thought at all from out of the essence of technology within which it belongs...
...Aspect (idea) names and is, also, that which constitutes the essence in the audible...
...the use of the word Gestell as the nà me for the essence of modern technology,...