I thought minimum sector altitude was the large numbers on each sector on a sectional chart indicating the altitude which will give you 1000 feet obstacle clearance in that sector.
On a Sectional Chart, that figure is called an "MEF" or Maximum Elevation Figure. This represents the highest known terrain or obstruction (the NOS calls these "features") in the quadrangle, and does not provide obstacle clearance.
IFR Low Altitude enroute charts also have similar figures. Jepp calls it a "MORA" (Minimum Of Route Altitude) and, the NOS calls it an "OROCA" (Off Route Obstacle Clearance Altitude). The OROCA and MORA provide 1000 feet of obstacle clearance in non-mountainous terrain (below 7000' MSL), and 2000 feet of obstacle clearance in mountainous terrain (above 7000' MSL). Also, Jepp prints the MORA figures that are above 14000' MSL in red, suggesting the use of oxygen, and the figures below 14000' MSL in green.
And, IFR High Altitude enroute charts have no such figures - they aren't needed, since their MEAs, unless stated at a higher altitude, are FL180.