Turin Kinglist: 6 years

Manetho:

  Africanus: 7 years

According to the Turin King-list, Netjerikhet's immediate successor, Sekhemkhet, identified by his personal name Djoser-Ti, ruled for only six years. The human remains found in the South Tomb of Sekhemkhet's funerary complex belonged to a two year old child and are thus very unlikely to have belonged to Sekhemkhet himself.

A relief in the Wadi Maghara in the Sinai showing Sekhemkhet as an adult slaying a foe is sometimes seen as proof that Sekhemkhet was an adult during his reign. Such stereotyped representation, however, should be seen for what they are: conform to the canonic way of representing a king, regardless of his actual physical state, age or even sex.

It is also not clear if Sekhemkhet and his predecessor, Netjerikhet were related. According to the Cairo fragment of the Royal Annals, Sekhemkhet's mother was named Batirites, but there are no known sources that mention her in relationship to Netjerikhet.

Sekhemkhet's funerary monument, the Buried Pyramid built to the south-west of Netjerikhet’s, was never finished, which may corroborate the short reign credited to Sekhemkhet by the Turin King-list. If it would have been finished, however, it would have been an even more magnificent building than Netjerikhet’s. 

When this monument was discovered, its sarcophagus was found sealed and empty. It does not appear to have been used, hinting perhaps at an untimely death for this king.
 

Sekhemkhet strikes down a foe on a relief found in the Sinai.

The entrance to the unfinished Step Pyramid of Sekhemkhet at Saqqara.