Leaving an answer here because the answer by spaff is incorrect.
Things actually get a bit more complicated
First of all, this has very little to do with spell speeds, as a summon itself does not have a spell speed.
The spell used for summoning the monster does, and there's no problem negating this with a card like 'Magic Jammer' or 'Solemn Warning'.
Once the monster is summoned successfully, a window opens in which you can react to the summon with cards like 'Bottomless Trap Hole' or 'Torrential Tribute'.
Note that this is not the same as chaining. These cards will start a new chain at that point.
Lastly, we have cards that negate a summon (e.g. 'Solemn Strike' or 'Black Horn of Heaven').
These cards cannot be use against other effects that would summon a monster (except if they specifically mention being able to negate that effect itself, such as 'Solemn Warning', which can do both)
So the kind of summon these cards can negate are called (in the case of a special summon, I'm ignoring normal or tribute summons here) inherent special summons.
These are summons that do not form a chain when performed.
This includes Synchro, Xyz, Pendulum, and Link summons. They also include contact fusions (e.g. Gladiator Beast fusions) and monsters like 'Cyber Dragon' or 'Black Luster Soldier - Envoy of the Beginning'