Hole resonant-tunneling diodes (RTD) with Si/strained Si1-xGex heterostructures epitaxially grown on Si(100) have been fabricated and improvement in negative differential conductance (NDC) characteristics for high Ge fraction such as x = 0.5 was investigated. It is clearly shown that SiH4 exposure at low temperatures of 400-450 degrees C just after Si1-xGex epitaxial growth is effective to suppress surface roughness in atomic order. In the case of the RTD with x = 0.48. NDC characteristics for 1.4-nm thick Si barriers were observed at higher temperatures around 270 K than that for 2.4-nm thick Si barriers. By increasing the Ge fraction to x = 0.58, NDC characteristics were also observed at higher temperatures around 290 K than that with x = 0.48. (C) 2009 Elsevier Ltd. All rights reserved.